1. Field of the Invention
The invention pertains to blow molding apparatus, and particularly the blowpin assembly utilizing a shearing edge for shearing the neck of the molded article at the termination of the molding process.
2. Description of the Related Art
During a blow molding process wherein a hollow article is formed by expanding a synthetic plastic material against the surfaces of the mold cavity by compressed air, a blowpin assembly is utilized to seal the neck of the article being formed, inject the air into the article during molding, and sever or trim the neck of the finished molded article to permit release of the article from the mold.
In most blow molding operations, bottles, or the like, are being formed, and the blowpin assembly is inserted within the mold within the synthetic plastic blank which is to be inflated and formed. The mold neck portions are radially brought into position in opposed radial relationship to the blowpin assembly, and the blowpin assembly includes an air seal which cooperates with the mold neck to restrict the escape of air from the mold cavity during the inflation process. After molding, the blowpin assembly is axially withdrawn from the molded article, and the assembly includes an annular shear edge which cooperates with a circular shear opening defined on the mold neck forming parts to sever the molded article during the withdrawal of the blowpin assembly. Accordingly, upon the opening of the primary mold cavity and neck portions, the formed article may be readily removed.
Blow molding processes are used to form milk bottles, detergent bottles and other receptacles formed by high production blow molding processes, and the continual wear imposed upon the blowpin assembly shearing edge as it cooperates with the mold opening to shear the article causes the shear edge to rapidly wear and dull, requiring frequent replacement and sharpening. Such wear occurring at the blowpin assembly shear edge is a primary reason for blow molding process down-time and maintenance, and as the dulling of the shear edge of the blowpin assembly will result in ragged bottle neck edges and prevent proper release of the formed bottle or receptacle from the mold, it is of utmost importance that effective and clean shearing of the molded article occur as the blowpin assembly is withdrawn from the mold cavity.
Heretofore, the need to terminate the molding process for replacement of the blowpin assembly shearing edge has been considered a necessary deficiency with the apparatus, and operators of blow molding apparatus have lived with the expense of frequently replacing the blowpin assembly in order to have a sharp and effective shearing edge.